This application claims the priority of German application No. 198 16 647.8, filed Apr. 15, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an apparatus for improved contrast in a motor vehicle heads-up display.
Heads-up displays are known as systems for displaying information. Initially, these systems were used mainly in aircraft technology for displaying to the pilot information concerning the operating condition of the aircraft. Such heads-up displays produce an image of the displayed information, which can be recognized by the pilot directly in his field of vision. As a result, it is not necessary for the pilot to direct his eye away from the environment toward the instrument panel in order to read the displayed information. For some time, it has also been known to use such systems in the field of automotive technology. Images of the information to be displayed are produced in the driver""s field of view through an optical system.
Problems can arise if the ambient brightness is high. Due to the subsequent reduced contrast between the displayed information and the background, the displayed information can become difficult to recognize and read. From SAE Paper 920600 (pp. 21 to 27, especially p. 25), it is known to avoid this problem by varying the brightness of the displayed information according to the ambient brightness. For example, in sunlight the information is displayed more brightly than it is in darkness.
Furthermore, in German patent document DE 41 16 043 C2, reference is made to Japanese patent publication No. 02-58284 which shows that a portion of a windshield is dark-colored, and displayed data are made visible by a heads-up display in which the windshield is darkened. This darkening can be achieved by tinting the windshield or by applying a film for this purpose. The windshield is thus, from the driver""s viewpoint, dark-tinted within a certain angular range of view. Data presented in a heads-up display are visible for the driver within this specific solid angle.
German patent document DE 42 42 797 C2 discloses a display of information by means of a holographic plate. According to this document, to improve contrast the back of the hologram is tinted dark.
It is an object of the present invention to improve the readability of important data presented by means of a heads-up display.
This and other objects and advantages are achieved by an apparatus for improving the contrast of a heads-up display in a motor vehicle, in which important data are visible in the specific angle of view, while other data are visible in the straight-ahead direction.
It proves advantageous that the information for the driver is always visible at the same location. In the case of the important information (such as the vehicle""s speed), the assurance is given, on account of its display in front of the darkened background, that it is generally readable regardless of the light conditions.
In a preferred embodiment according to the invention, the data indicated by the heads-up display is shown to the driver in the straight-ahead direction, while important information such as speed (or the like) is displayed in the lower, dark area of the windshield (area 3) and comparatively unimportant information, such as minimal interval, navigation indications (or the like) are displayed in the upper field (area 4).
Thus the driver can, under normal ambient luminous intensities, read the information in both windshield areas. If the ambient luminous intensity increases, the driver can no longer read unimportant information in his immediate field of view, but the important information is still easily readable in the lower display area.
The specific solid angle in which the windshield is darkened lies outside of the usual field of view of the driver which the driver must usually see while driving a motor vehicle. In comparison with other common display apparatus involving a combination instrument integrated into the instrument panel, an advantage is gained in that the driver need only change his line of sight by a small angle in order to be able to see the information. Furthermore, by using the heads-up display the advantage is retained in that the focusing of the eye, which usually approaches infinity when observing the surroundings while driving a vehicle, requires hardly any change. Nevertheless, sufficient contrast against the background is provided in the displayed information, so that the information can be seen easily at all times.
In another advantageous embodiment according to the invention, information is shown in a heads-up display in the driver""s straight-ahead view and important information is still visible to the driver within the specific solid angle. Thus, in normal ambient light, the information is displayed for the driver without requiring a change in visual accommodation within the customary field of view. If the light conditions change such that the information is poorly or not at all visible on account of the lack of contrast with the ambient light, the driver can read the information with sufficient contrast in the specific solid angle.
In the previous embodiments according to the invention, it is advantageous that the area of the dark portion of the windshield is limited. The readability of important information is assured quite independently of light conditions. At the same time, in the embodiments the possibility is provided for making a great number of data displayable.
In a further embodiment according to the invention, the windshield seen by the driver is dark-toned in the lower area of the windshield. This area proves to be suitable since the driver can read the information simply by lowering his line of site, although this area usually must not be viewed while driving a motor vehicle.
In yet another embodiment according to the invention, the area of the windshield is tinted by impressing the tint onto the windshield by a printing method. This method of tinting is known and is already used in order to produce a darkened strip in the upper area of windshields of motor vehicles. This method can be used in order to advantageously darken the windshield in the appropriate area.
In still another embodiment according to the invention, the area of the windshield is tinted by tinting the inner layer of the windshield in an appropriate area. The film forming the inner layer can likewise be tinted comparatively easily within a certain area.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.